Re: Heavy 7mm Projectiles
More bullet options are never a bad thing, I totally agree!!! That said, I have yet to see a rifle set up for the 200 gr ULD RBBT not shoot them very well, impressively well to be honest.
Your case should be just slightly less potent then a 7mm RUM. I think you will get your 3K fps with top loads. THe RWS brass is pretty stout stuff so you should get there without to much trouble.
A 1-8.25 should easily handle that bullet in any conditions at the velocities you will be shooting in. Just make sure bullet baring surface compression by the lands is less then 20% or you may run into problems which I think we have already talked about.
I have used 1-9 twists in every thing from the 7mm STW to my 7mm AM with these bullets and will say that out to 600-800 yards I have yet to see a problem in accuracy or consistancy.
Past that, with the 1-9 twist barrels, accuracy seems to drop off noticably. Not dramatically but enough that at 1K I would not take a shot at a deer with my lightweight 7mm AM which shoots these bullets to 3150 fps comfortably in a 27" barrel.
I can not say for 100% this is a stability issue or the fact that all the rifles I have shot these at that range with were light weight rifles and that just makes shooting them at longer ranges more difficult.
I can say I have shot a 1-9 4 groove barrel at these ranges in my 7mm AM with these bullets and accuracy was extremely good. That was a 34" pipe and velocity was in the 3350 fps range. You will have to ask Buffalobob about that rifle, its his!!
I have been working with Rock barrels on a special thin land 5R rifling design for this specific bullet and we have settled on a 1-8.7 twist as being just about as perfect as we can get for the 7mm AM.
FOr your round, I would probably say a 1-8.5 would be totally adiquate for your needs but you will never see any issues with a 1/4" more twist at these velocity levels and in cool temps and high humidity, it will just give you that extra spin to make sure things stay on point at long range.
I have no problem listing what I have found for BC testing these bullets in my rifles. That is because I state these numbers as what I have found measuring actual bullet drop over 1K yards. These are not what many would say are scientifically pure BC numbers but when you plug them into the ballistic programs, I can hit what I am shooting at out to very long ranges so something is working.
I use .900 for a BC on my heavy 7mm AM rifle(3300 fps) and .88 BC for my lightweight 7mm AM(3150 fps). My customers have reported BCs ranging from .780 to .920 depending on the velocity they are using, altitude they are shooting at and pressure and humidity values.
TO get started with your velocity levels from what I have seen in rifles such as the 7mm STW and the like, I would start with a BC of .850 to .880 and tweak it from there. They will most often get you within 1 to 1.5 moa at any range with these values to start with.
Now to those of you that want to raise hell with these numbers, remember, these are only the numbers I have to plug into my Exbal program with my muzzle velocity and three acutal down range impact measurements from zero to get my prejected ballistic model to match up to actual bullet flight so take that for what you will. [img]/ubbthreads/images/graemlins/grin.gif[/img]
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